1. Field of the Invention
The invention relates to a diagnostic device that diagnoses a state of a fuel cell.
2. Description of Related Art
A fuel cell system is known that is provided with a fuel cell in which a plurality of cells generating electric energy by using an electrochemical reaction of an oxygen gas and a hydrogen gas are stacked and an output control unit which generates an alternating current and an AC voltage in an output of the fuel cell (for example, refer to Japanese Patent Application Publication No. 2013-140715 (JP 2013-140715 A)).
This fuel cell system is provided with an impedance calculation unit and a hydrogen concentration calculation unit. The impedance calculation unit obtains an absolute value of an internal impedance of the fuel cell as a whole based on the alternating current and the AC voltage output from the fuel cell. The hydrogen concentration calculation unit calculates a hydrogen concentration of the fuel cell based on the absolute value of the internal impedance of the fuel cell.
In addition, in a fuel cell system that is disclosed in Japanese Patent Application Publication No. 2012-252986 (JP 2012-252986 A), a deficiency or non-deficiency in the oxygen gas or the hydrogen gas is diagnosed based on an impedance of any of the plurality of cells and the amount of a decrease in an output voltage of any of the plurality of cells.
Specifically, the impedance of any of the cells is measured, and then it is diagnosed that the cell is deficient in either the oxygen gas or the hydrogen gas when an absolute value of the measured impedance has increased. In addition, it is determined, in accordance with the amount of the decrease in the output voltage of the cell, whether the cell is deficient in the oxygen gas or the hydrogen gas.
In the fuel cell system that is disclosed in JP 2013-140715 A, it cannot be diagnosed for each of the cells whether the cell is deficient in the hydrogen concentration although the hydrogen concentration can be calculated with regard to the fuel cell as a whole.
The fuel cell system that is disclosed in JP 2012-252986 A requires the amount of the decrease in the output voltage of any of the cells, in addition to the absolute value of the impedance of the cell, for whether the cell is deficient in the hydrogen gas or the oxygen gas to be determined.